Old TV x-ray exposure
 

After just posting a thread in the general topics forum on shoe fluoroscopes (which some of you may remember from years ago), it got me thinking: Many of the old TV repair books caution you from getting too close to the front of the screen when the TV is on. Was this just an "old wives' tale" that was proven generally unfounded later on, or did the old sets actually emit more x-radiation than modern sets do? It seems you don't hear that warning too much anymore.

Yes, the older TVs did emit more X radiation. Just stay more than 3 feet from the screen; the air will stop it. It really isn't that dangerous; I've been working on TVs for decades and I'm perfectly normal (it's everyone else who is screwed up).

When I was growing up (well, to the extent that I ever did...:D ), my parents always insisted that we stay at least five feet from the TV screen, because it was "dangerous" (the X-ray thing) and "would wreck our eyes". Not sure about the X-ray issue (although if you think about how X-ray tubes work, it is a VERY reasonable possibility that TV tubes could emit some of those frequencies, too), I think they were right about the latter, for sure, judging from how computer screens at close range tire the eyes!

From what I recall, legislation mandated X-ray protection via lead shielding on the picture tubes made after around 1970 or so. Other tubes emitted radiation as well.
http://hps.org/publicinformation/ate/q498.html
http://hps.org/publicinformation/ate/q4212.html
Tom

Xray radiation is related to anode voltage, so the main risk was from color sets, which use 20-25 kv. The radiation was both from the CRT and the hv shunt regulator tube.

B & W sets, which typically used 10-15 kv, were not an issue.

The main risk in a non-defective set was to servicemen running the sets with shielding removed and being constantly exposed day in and day out. The main risk in defective sets was from a defective regulator or rectifier tube (can't remember if it was either or both). The defect was a tilting of the internal parts of the tube, which allowed X-rays to be emitted around the metal parts in the bottom of the tube. Which side of the set would be "hot" depended on the mounting of the emitting tube. In some sets, this would be downward, so a kid sitting up close with feet under a consolette would get exposed. The tube problems were discovered and voluntarily reported by the manufacturer in parallel with instituting new QC measures to prevent defective tubes from being manufactured or sold. Even though the problem was fixed immediately as it was discovered, additional tests were added for all TV sets. I recall tests being done when I was at Motorola, but in general, the levels were so low as to be hard to measure. The introduction of solid-state rectifiers along with greater X-ray blocking in CRT glass eliminated the problem for good. (Now, of course, there are questions about CRT disposal because of the high lead content.)

Xray exposure at the face of the tube didn't seem to be an issue. I have mentioned before about a service manual for an Admiral set that used the 21AXP22 and they warned about soft xrays at the center of the screen, but that the safety glass was enough to stop them. I guess some of the early bw projection sets ran voltages high enough for this to be an issue...I seem to recall a discussion of that some time ago on here. I have heard of figures like 40-80KV in some odd applications.

It would seem a metal cabinet set would be safest to protect from the HV tubes. There is a website out there featuring Xray photographs taken with the aid of, IIRC, a HV regulator. Kinda eerie.

GE was a company that had trouble with a few late 60s color sets going over the limit. They more than made up for it, switching to a lead-encased HV rectifier (3AT2?) and plastering the inside of some models with a big, bright radiation symbol to catch the attention of, I guess, DIY'ers.

I don't think there is much to worry about for us as hobbyists. I don't recall ever hearing about an epidemic of cancer among TV repairmen.

Sorry to resurrect an old thread, but a response posted recently to another thread

caused me to do a lot of thinking recently, on that restoration project. (B&W Projection TV, 5” tube, 40K Anode voltage.)

My question is, do any old vets out there really have any recommendations to share, with respect to X-Ray exposure? I’ve already taken just about every other precaution I can think of, including insulated workbench & workspace, isolation transformer, and a big sign that says “ONE HAND IN THE POCKET AT ALL TIMES” hung on the wall.

Please don’t tell me I also need to get leaded glass goggles and lead lined underwear too, to keep my eyeballs (and other balls) from falling out/off from working on this. I do want to fix this thing up, but I’d prefer not to die trying. :-)

I can deal with High Voltage, I've done that since High School. But X-Rays?

It's kinda funny but i Have 3 old crt projection units, 2 barco, 1 bell and howell, all of these projectors have a thin sheet of lead either around the CRTs or around the the cabinet. I think on your b&w projector there is a lead coating painted black on the rear section of the crt. Logan

electrons subjected to a voltage potential accelerate. accelerating electrons emit x-rays. are the x-rays generated by a CRT worth worrying about? probably not.

It's the deaccelerating electrons we have to worry about...

The Bremsstrahlung effect, a contraction of the German brems for braking, and strahlung for radiation produces the x-rays.

a facinating read:
http://en.wikipedia.org/wiki/X-ray_tube

99 percent of the electron's energy goes towards heating the anode.

The crt glass is thick, and the extra lead mixed in stops it all. The regulator tubes had the thin pure glass envelopes that allowed more out.

Sitting back is/was more about eyestrain....

Hmmm. Is that why my friends say I have such a glowing personality??? :D:yes::banana::scratch2::thmbsp:
Bill Cahill :lol:

How about a 3DR3 in its nice lead jacket? It has, printed on the side: "X-Ray warning -- This tube in operation may produce harmful radiation unless it is shielded". The lead coating is about 1/8" thick, and there is a removable paper warning that says "Caution: Contains 55% Lead Oxide, Toxic by Ingestion". I'm guessing it is from the tail-end of tube-production years, when we were all getting more paranoid about what television could do to us!

--Bob

Almost a year to the day, I found this thread.

Wondering if any news has surfaced on this issue.

IMO, I'd be slightly more concerned about the EMF from the deflection yoke. X-ray emission in a post-70s set are probably very small.

I don't think there's any risk from any X-rays from any TV. It's all a bunch of propaganda to facilitate lawsuits against TV manufacturers back then. Everything on Earth and in the universe can cause cancer, according to all collective research. We're all going to die. Some of us will die after a fulfilling, fun, care-free life; others after hiding from everything and living a sheltered, boring, ultra-safe life. Guess which way I'm seeking? Both of my friends who died young recently were vegetarian health nuts, and were scared of every new "health threat" conjured up by the media.

Charles

What you think or do not think about any technical problem is irrelevant.
The actual physics is what matters. X-ray emission by electrons being
decelerated is a fact of life, and unless you can confirm what you claim
with reliable measurements, I consider it prudent to avoid spending too
much time near the high-voltage circuits of a large color CRT set.

I've never heard of any cancer cases linked to TV x rays.

FWIW, RCA says anything above 16kv (absolute) is suspect, but even then, you're talking so far on the weak end of the spectrum, that it's doubtful the x rays even get anywhere.

25kv at 2 or 3 ma really isn't much in the realm of x-rays...

Keep the HV box closed and don't stare at that funky 6BK4 too long, and you'll be fine. You're more likely to get zapped than anything else...

Good point made here. Electrocution is probably a bigger risk than x-ray radiation. However, back to my point on yoke emf's...Since the CRT's tended to get bigger, and very few yokes are shielded in any way (copper windings all exposed) this could be an even bigger concern than x-rays. Think about it, all the cabinets were plastic after a certain point, removing any potential for shielding there. The sides of a set may be really 'hot' with low-frequency EM radiation. Whether or not this is irrelevant health-wise doesn't concern me much. Just curious about it all.

Last year sometime, a friend came over with a radiac meter, and we measured the x-ray output from the screen of my CTC-4 through the safety glass. On white screens, we measured a maximum of .4 millirems/hour. Strange that the max wasn't recorded on black screens when HV is at max 25KV.
We informed a member of our museum, who is an x-ray technician, and he said "that's pretty high". The three foot rule sounds prudent, but I wouldn't worry about it too much.
Kevin

Actually that makes sense. The maximum x-ray energy will be related to the HV. But, the x-ray flux will be proportional to the current. You'll have a higher flux of x-rays on a white screen even though the maximum x-ray energy will be lower.

John

I heard that IC's (integrated circuits) release a cancer causing frequency when paired with all forms of flat screen television, and even more particularly dangerous when mixed with digital broadcasting in color. Thus, a vintage, tube type, analog, black and white, television set is the ONLY healthy way to view the crap they call TV shows these days.

Spread the word before its too late!!

That's my point... Nobody has quantified nor qualified/disqualified what strengths of X-rays may or may not be harmful... I'm speculating on the experts' speculation :scratch2:


In the meantime, I'll take my chances. I race motocross, and I drive on the Los Angeles freeways, so I don't think X-rays will get the better of me, myself. A friend died of lung cancer last year, and she never smoked, nor lived with a smoker, and she was a fitness nut in perfect physical shape. If your number is called, that's it.

Charles

I assume the Radiac was a model 440 ionization meter. If so, you have to be careful interpreting results near the face of a CRT. The static charge on the surface can cause a false reading in the extremely sensitive electrometer.

I decided to try the same test. I used a Victoreen model 450B ionization counter. It is sensitive down to 0.01 mR/hr for x-rays above 7KeV.

I tried it on a 1949 Sylvania that has an anode voltage of 9.5KV. I measured nothing, but didn't expect to measure much. The end point energy would be close to 9.5KV but the yield above 7KeV would be low to start with and the glass attenuates most of it.

I tried a color CRT monitor with the same result. I thought my 42" rear projection might let me pick something up near the CRTs, but I didn't see anything there either.

At work I use an electron beam evaporator that runs at 10KV and has a maximum current of 1.5 amps. I was concerned that some damage I was seeing in foils that I was coating might be due to an x-ray dose. I put a personal dosimeter in the chamber. At 0.3 amps it maxed out the dosimeter. I had to do a very short run to even get the measurement on scale. This would have been a serious dose to a human.

I tried doing measurements outside of the chamber which is constructed of aluminum and has glass and acrylic windows. There was no detectable radiation outside of the chamber, even through the plastic window. x-rays of this energy are easily shielded. At 25KV the story would be a bit different. But I doubt that even the old roundies present much of a hazard. I think you would see more near the HV rectifier tube, but no one wants to get close to that anyhow.

John

John, Maybe you could toss a dosimeter into a couple of hv cages , near the HOT, taped to the screen etc to determine some relative radiation levels in these old sets.

Kinda reminds me-does anyone know why every 1k3 hv recitifer I have ever come across has x-ray warnings screen printed on the tube, while the old stand by equivalent 1B3 doesn't boast any such warnings?

Actually, I've seen it on 1B3s, too.

I think the 1K3 has a higher anode voltage rating, so it would have gone into higher voltage sets.

Though, just about everything used a 1B3, didn't it?

Another dosimeter taped to the face of the CRT (lower portion of the screen, so it doesn't much interfere with watching TV shows) would also be interesting. I assume that these things are cheap enough to expend casually.

All I know is that I sat waaaaay too close to the TV when I was a kid and that my third eye works just fine.

I'll see what I can do. We always have extra film badges, but they may have to pay processing for each one turned in. If so, hopefully they'll consider this a part of "Outreach."

John

Here's a table and graph of x-ray attenuation in pyrex glass.

http://physics.nist.gov/PhysRefData/...Tab/pyrex.html

If you take the attenuation coefficient and multiply it by the density of glass in g/cm**3, take the reciprocal, you get the thickness of glass required to attenuate the x-rays by a factor of 2.7

For 8KeV x-rays, this is 0.014cm or 0.0055". It doesn't take much to shield them.

For 20KeV x-rays it's 0195cm or 0.077". Quite a bit more and leaded glass is now needed to protect you.

John

OK, so.....:scratch2:we're going to live watching our old TV's......:scratch2:
right?

Been fine so far haven't we? If I start glowing green, then I'll worry. The radiation from these sets is nothing compared to the things I've done and ingested in my life. I wouldn't worry too much. Like others have said, just limit exposure, use common sense and stay away from the 6BK4!:D

The dose we get from a dental x-ray or a CAT scan is much higher than what we'd ever accumulate from watching TV. We get dental x-rays because the benefits outweigh the risks. Exposure to x-rays changes the probability that you'll develop a cancer or other issue. It's still a roll of the dice. There's no clearly defined point at which you go from being ok to not being ok.

Some of the risks we encounter are regulated. Others are left up to us to decide about.

There are lots of things in life that entail some risk. Nearly every activity. We make our own risk/benefit evaluation when we choose to participate in some activity.

I wouldn't use a running CRT as a pillow to sleep on, but I'm not about to stop watching TV because of a nearly unmeasurable increase in risk.

For me it's not just the length of my life but also the quality of that life. Gotta have a balance between the two.

John

I like well-done (almost burnt) toast. Years ago, someone told me it was likely to increase my chances of getting cancer.

Hmmmm


well maybe one of you with a crt screen can tell me what the HV is on this schematic. I have this TV but always worried about the X-rays. But it has glass shielding and if the Hv is low enough I really won't be worried.

Oh and why do I think yo can read it if I can't?? :scratch2:

Thats because when I printed this, and tried reading it really hard, I just couldn't make out the value of one capacitor.(on my lcd monitor)

But then one day I scrolled by the schematic on my Front Projection Display(CRT) and It was clear as day. .0047 MFD.

So maybe one of you with a far superior CRT monitors can take a peek at it for me?? :D

Cheers,
Rudy

V18 V19 and V20 are your HV tubes (sweep, rectifier and damper). At least V19 and 20 should be inside of the HV cage, which is more than enough shielding for them. I wouldn't worry, though. Sitting close enough to the set to get anything close enough to a dose of rads would damage your eyes from severe strain before that would happen.